Bloody bastard fungus gnats on houseplants. Resorting to nemotodes?

[OneArepa]

I’ve got four shelves of cuttings and mixed mature plants and these intruders are now making themselves right at home. Never had more than one or two before but this lot seem especially persistent buggers. The plants are by a dining table so I’m really not happy to host these visitors. I’ve moved half of the plants out for now.

So far I’ve tried Ecofective bug spray and a neem oil / washing up liquid solution. No joy. No grit down yet but have ordered some, plus sticky stalk fly paper thingies from Amazon.

I’m trying not to resort to nemotodes because bleurgh, although I’d choose that option over really harsh pesticides.

Can I have a sense check on this all, please? I know it’s spring so prime season. If I need to use nemotodes, anything I should know (bar fridge / only order when needed / possibly don’t watch too closely)? How long would they actually remain in the compost themselves?

Many thanks

I haven't tried grit as I had them in my seedlings - just wouldn't be practical. I found the fly trap paper things extremely effective - I just wound them around the trays, left them overnight, gone.

In terms of trying to avoid getting them in the first place, you're meant to keep compost bags tightly sealed which I do now.

Thanks, Pootles. Promising to hear you had such good results with the paper. Bit worried about larvae still in the soil. Annoying generally as I had the bag firmly rolled and taped down after opening!

Nematodes are wonderful things, why the aversion? I think I might be ordering some myself for the same issue shortly, always use them outdoors but am definitely seeing fungus gnats on the houseplants at the moment, grrrr.

I use the sticky fly trap things, they cleared up the gnats quite quickly.

I thought nematodes were microscopic so you wouldn't see anything bleugh? Happy to be corrected on that tho...

Rhinestone I saw one article saying if you look very closely you can see a shimmering effect and then the teeny ones emerging at the surface. Pleased you also had joy with the sticky traps!

Whitney honestly, I can eat dinner while watching surgery documentaries, no bother, but anything involving tiny things with antennae or many legs… I’m less good! Do you happen to know how long they stay in the soil after it’s treated?

Do you mean sciarid flies? We had a big infestation in houseplant compost over the winter and I got nematodes. It was literally the best thing I ever did! Within 3 days of application they were gone.

They’re the ones. I might have to just get some if it’ll solve things that well.

Nematodes are fab, but only watering from below (pour the water into the plant tray so the surface compost is always dry) and putting down a plant collar of paper or card smeared with a layer of vaseline to get rid of existing gnats also works.

What about a couple of sundew plants placed alongside them? Dependent on it being the right conditions for the sundew, of course.

Backflanded that would definitely be an interesting option! Some of the rosette-type Droseras look good. Not one I’ve ever had before. Will have a Google.

Gliblet thanks - definitely sticking to watering from below going forward.

You’re getting a lot of flies at the moment because the grubs in the soil are metamorphosing into the adult fly, so they can disperse and lay eggs in other pots. So every time you kill some, another batch will emerge from the soil.

what I would suggest is a) empty out all your pots, shake off all the soil from the roots, make sure you’ve removed any transparent grubs, then repot in fresh compost b) make it a habit to cover the soil surface in any pot with a layer of gravel, fine grit or even sand, so the fly is not attracted by the prospect of humus rich moist soil.

yes, Drosera is good for fungus gnats. Butterworts are better for whitefly.

Mere such a faff as none of them are otherwise remotely due but I do prefer this option to nematodes, though! Thanks for the extra info.

I had an infestation recently which seemed related to a bag of Verve houseplant compost (have since seen loads of reviews saying the same!)
I did watering with hydrogen peroxide, letting soil dry out and watering from below and also a layer of grit on top. Seems to have worked!

That’s interesting - the only change I’ve made recently is potting some cuttings on. It was Miracle Gro houseplant compost, though.